The invention relates generally to computer based audio control systems and more particularly to computer based audio control systems utilizing adaptive compression and adaptive filtering in multimedia computers.
With the proposal of increased video and audio applications in multimedia personal computers, a user can potentially use the computer to control the television, telephone and home stereo as well as connect signals from cable television links, satellite TV and various other video/audio sources such as compact disc (CD) players, VCRs and digital versatile disc (DVD) players to the home entertainment system. The variety of audio sources and differing formats requires measures to ensure suitable audio delivery. For example, audio from a telephone line will contain low resolution voice data. A DVD may provide a movie soundtrack. A broadcast TV signal may have a movie soundtrack with a compressed dynamic range. A CD may provide high-definition music. DVDs can be recorded in a plurality of different audio formats containing compressed audio or uncompressed audio and multichannel surround sound formats for theater entertainment systems. For example, a DVD disc may be recorded in 96 kHz, 44.1 kHz, 48 kHz, mono, stereo, multichannel, AC-3 encoded, MPEG-2 encoded, DTS encoded, SDDS encoded, HDCD encoded, and other formats. Each type and format of audio will have different characteristics and may require different compression and filtering which are not generally accommodated by conventional multimedia computers.
Some high-end home entertainment systems have multichannel audio systems, such as surround sound systems with three or more channels to provide theater sound effects. The surround sound channels are often presented at a lower volume level than front channels since movies contain most of the audio information in the front channels and use the surround channels sparingly as effects channels. A typical surround multichannel system may include six channels. These channels typically consist of a left, right and center front channel, a left and right surround channel and a subwoofer channel. Differing prerecorded equalization settings among surround channel recording or among the various formats can sound different on the same speakers.
When hearing sound, the human ear has a frequency response that typically attenuates certain frequency bands at lower and upper frequencies, for example below 200 Hz and above 10 kHz. Furthermore, this frequency response is not consistent over different volume levels. There is less attenuation in the low and high bands when the volume of the sound presented to the ear is increased. This leads to an inconsistent listening experience when listening to material at different volumes, especially when the material is created to be listened to at a specific volume level.
For example, it is not always suitable to listen to a movie at loud levels. Movies and television programming can be mixed for fairly loud listening environment and may sound very different at low volumes. The original mixing becomes more problematic with multichannel information. For instance, when playing a movie at a low volume, a listener can hear the loud dialog but whispers may often be inaudible. During television programs, when commercials are played, they can seem excessively loud because they are already compressed. Compression of channels can help even out levels but this will cause noticeable distortion in compression sensitive material such as music. Music or sound effects in surround channels of a multichannel system can also sound proper at loud volumes, but can obscure the vocal channel at low volumes. Therefore it would be advantageous to adaptively control compression and attenuation independently in each channel. Information in different frequency ranges do not attenuate in a consistent fashion due to the physical limitations of the ear, or the ear frequency response. Consequently turning down or reducing volume appears to attenuate low and high frequencies more than mid range frequencies.
Therefore there exists a need for an adaptive audio signal compression and attenuation computer system which can provide independent compression for each channel if desired. It would advantageous if such a system took into account the physical limitations of the ear to properly compress and filter received audio on a per channel basis.